Complementary metal oxide semiconductor (CMOS) technology, employing complementary n-channel and p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs), is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits. CMOS technology is also used for analog circuits, such as image sensors (e.g., CMOS sensor), data converters, and highly integrated transceivers for many types of communication.
The words “complementary,” “n-type” and “p-type” refer to the fact that the typical digital design style with CMOS use complementary combinations of MOSFETs that have charge conduction channels that carry negatively charged electron electrons, commonly known as “n-type,” and MOSFETs that have charge conduction channels that carry positively charged holes, commonly known as “p-type.”
Two important characteristics of CMOS devices are high speed and low static power consumption. Since there is always one transistor in series that is in its off state under static conditions, CMOS circuit elements draw relatively little power under static conditions. Only momentarily during switching between on and off states is power consumption large. Consequently, CMOS devices do not consume as much energy and produce as much heat as many other forms of logic, for example, transistor-transistor logic (TTL) or NMOS (n-channel MOSFET) logic, which normally have significant standby current even when not changing state combined with significant voltages. CMOS also allows a high density of logic functions on a chip. It was primarily for these reasons that CMOS became the most widely implemented technology in VLSI chips.
Another characteristic of CMOS is that it is volatile in that once the power source is removed, the logic state is lost, both for CMOS logic circuit and CMOS based memory elements.
A characteristic of non-volatile memory is relatively large power consumption per bit as compared to logic.
Despite the benefits of CMOS, there is a need to continue to increase energy efficiency to enable still lower power circuits for mobile application and energy-hungry applications, as well as greater packing density, which can be limited by heating, for increased computational power in logic circuits. Moreover, with logic circuits frequently powered on and off as needed with logic states off-loaded to and retrieved from memory, non-volatile logic becomes attractive. Mechanisms for low-power non-volatile memory also are of general interest. With the advent of low voltage logic, as described herein or by other means, low power non-volatile memory operating on compatible voltage scale would be more beneficial still.